Jet loop reactor having nanofiltration

ABSTRACT

The invention relates to a device for the continuous, homogeneous-catalysis reaction of a liquid with a gas and optionally an additional fluid, wherein the device comprises at least one reactor having an external liquid circulation driven by a pump, and wherein the device has at least one membrane separation stage that preferably holds back the homogeneous catalyst. The aim of the invention is to specify a device that allows homogeneous-catalysis gas/liquid phase reactions, in particular hydroformylations, which operate with membrane separation of the catalyst to be performed economically at an industrially relevant scale. Said aim is achieved in that a jet loop reactor is provided as the reactor, and that the pump and the membrane separation stage are arranged in the same external liquid circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 14/343,917, filedAug. 6, 2014, allowed, which is a U.S. national stage application ofInternational Application No. PCT/EP12/067513, filed Sep. 7, 2012, whichclaims the benefit of priority from DE 10 2011 082 441.3, filed Sep. 9,2011, the entire contents of which are incorporated herein by reference.

The invention relates to a device for the continuoushomogeneous-catalytic reaction of a liquid with a gas and optionally afurther fluid, wherein the device comprises at least one reactor havinga pump-driven external liquid circuit, and wherein the device comprisesat least one membrane separation stage that preferably retains thehomogeneous catalyst.

A device of this type is known from Janssen, M., Wilting, J., Müller, C.and Vogt, D. (2010), Continuous Rhodium-Catalyzed Hydroformylation of1-Octene with Polyhedral Oligomeric Silsesquioxanes (POSS) EnlargedTriphenylphosphine. Angewandte Chemie International Edition, 49:7738-7741; doi: 10.1002/anie.201001926.

A liquid is a substantially incompressible free-flowing medium. A gas isa compressible free-flowing medium. A fluid is a liquid or a gas. Atwo-phase mixture of a homogeneously distributed liquid phase and a gasphase distributed dispersely therein is likewise a fluid within themeaning of this invention. On account of the gas fraction, fluids ofthis type are compressible to a slight extent.

In the context of the present invention, a supplied liquid is asubstance or mixture of substances which is present in the apparatusunder reaction conditions in the liquid state of matter and comprises atleast one reactant. Gas is taken to mean a pure gas or a gas mixturewhich comprises at least one reactant and optionally an inert gas. Anexample of a gas which comprises two reactants is the synthesis gas thatis used, for example, in hydroformylations and consists of hydrogen andcarbon monoxide.

A jet loop reactor in the context of the invention is a device for thecontinuous reaction of a liquid and at least one further fluid, in whichthe liquid enters under pressure through a nozzle into a reaction space,flows through this along a main direction of flow, is reversed at thereaction space end situated opposite the nozzle, flows back in theopposite direction to the main direction of flow and is againaccelerated in the main direction of flow, and so within the reactorspace an internal liquid circuit (loop) is established. The second fluidis entrained by the liquid stream and reacts on the path along the loop.The liquid thus serves as motive jet medium.

For introduction of kinetic energy into the liquid, an external liquidcircuit is assigned to the reaction space, in which external liquidcircuit some of the liquid is circulated outside the reaction space. Apump which provides the kinetic energy to the liquid stream which isnecessary for establishing the loop flow within the reactor is providedwithin the external liquid circuit. The nozzle is fed correspondinglyfrom the external circuit.

A good introduction into the technique of jet loop reactors is offeredin: P. Zehner, M. Krause: “Bubble Columns”, Ullmann's Encyclopedia ofIndustrial Chemistry, Electronic Release, 7th ed., Chapter 4, Wiley-VCH,Weinheim [2005].

In hydroformylation (also termed oxo reaction), hydrocarbons havingolefinic double bonds (alkenes) are reacted with synthesis gas (gasmixture of hydrogen and carbon monoxide) to form aldehydes and/oralcohols.

Fundamental introductions into hydroformylation are offered in Falbe,Jurgen: New Syntheses with Carbon Monoxide. Springer Verlag 1980,Berlin, Heidelberg, New York and Pruett, Roy L.: Hydroformylation.Advances in Organometallic Chemistry Vol. 17, Pages 1-60, 1979.

Hydroformylation serves for producing higher aldehydes. Higheraldehydes, in particular those having 3 to 25 carbon atoms, are used,for example, as synthesis precursors, for producing carboxylic acids,and as aroma substances. Technically they are frequently converted bycatalytic hydrogenation to the corresponding alcohols which in turnserve for producing plasticizers and detergents. Owing to the commercialimportance of hydroformylation products, the oxo reaction is carried outon an industrial scale.

In commercial hydroformylation, now, organophosphorus metal complexcatalysts based on cobalt or rhodium are used. The catalysts aredissolved homogeneously in the liquid hydroformylation mixture. In thecontext of separation of the target product (the aldehydes) from thehydroformylation mixture, the homogeneous catalyst must also beseparated off gently from the hydroformylation mixture, since thecomplex catalyst reacts in a comparatively sensitive manner to changesin state, and could lose its activity.

Traditionally, the catalyst is separated off from the hydroformylationmixture by distillation. In order to decrease the risk of deactivationand to lower energy consumption of the process, recently there have beenefforts to separate off the homogeneously dissolved catalyst from thehydroformylation mixture using membrane technology (nanofiltration).

The fundamentals of membrane-supported organophilic nanofiltration forseparating off homogeneously dissolved catalyst complexes fromhydroformylation mixtures are described by Priske, M. et al.: Reactionintegrated separation of homogeneous catalysts in the hydroformylationof higher olefins by means of organophilic nanofiltration. Journal ofMembrane Science, Volume 360, Issues 1-2, 15 September 2010, Pages77-83; doi:10.1016/j.memsci.2010.05.002.

In the membrane filtration of reactor discharges from hydroformylations,dissolved or non-dissolved synthesis gas frequently in the liquidreactor discharge is a peculiarity: Hydroformylation is a two-phasereaction, hydrogen and carbon monoxide form the gas phase, the alkenes,aldehydes and alcohols form the liquid phase in which the catalyst isdissolved so as to be solids-free. Part of the synthesis gas is alsodissolved in the liquid reactor phase in accordance with the dissolutionequilibrium in the reactor and is taken off together with the reactordischarge. As long as the synthesis gas remains dissolved in the reactordischarge during membrane filtration, the membrane filtration is to thisextent problem-free. If, however, the liquid reactor discharge isaccompanied by a gas phase, or if a gas phase is formed as bubblesduring expansion at the membrane, the gas bubbles may be able to damagethe membrane mechanically. Polymer membranes are particularlysusceptible to damage by gas bubbles.

A further problem due to outgassing synthesis gas is the loss of carbonmonoxide: In particular in the Rh-catalyzed hydroformylation, the COpartial pressure exercises a critical effect on the activity andstability of the catalyst complex. In order to avoid the loss ofactivity during the membrane separation of homogeneously dissolvedcomplex catalysts from the reaction discharge of a hydroformylation,EP1931472B1 proposes ensuring a minimum partial CO pressure at all threeconnections of the membrane separation stage (feed, retentate,permeate).

WO2010023018A1 shows two jet loop reactors connected in parallel to oneanother having a shared external liquid circuit. The jet loop reactorsare used with homogeneously dissolved catalysts in the hydroformylation.Separating off the catalyst is not thematized.

Janssen, M., Wilting, J., Müller, C. and Vogt, D. (2010), ContinuousRhodium-Catalyzed Hydroformylation of 1-Octene with PolyhedralOligomeric Silsesquioxanes (POSS) Enlarged Triphenylphosphine.Angewandte Chemie International Edition, 49: 7738-7741. doi:10.1002/anie.201001926 describe carrying out a homogeneously catalyzedhydroformylation in a special spray mist reactor which has two externalliquid circuits contacted to one another in a crossflow chamber. In afirst circuit, the liquid reactor discharge with synthesis gas dissolvedtherein is taken off from the reactor and circulated by means of arotary vane pump. In a crossflow chamber, the reactor discharge isdivided into two substreams: A first substream containing the liquidreactor discharge with dissolved synthesis gas as synthesis gas in gasphase is conducted along the first circuit back into the reactor. Asecond, purely liquid substream is transported by means of a pumpthrough a ceramic membrane separation stage. There, the target productis taken off as permeate, the catalyst-containing retentate is passedvia the second circuit strand back to the crossflow chamber and theremixed with the first liquid circuit. The advantage of this device isconsidered to be that the reactor discharge is degassed within thecrossflow chamber and therefore any separating gas phases remain in thefirst circuit. This is because the particular flow conditions of thecrossflow chamber favor a takeoff of the gas bubbles into the return ofthe first circuit. The second liquid circuit in which the membrane isarranged thus remains gas-free (this means H₂ and CO remain dissolved inthe liquid). However, the disadvantage of this laboratory apparatus isthe comparatively complicated structure thereof, the requirement for twopumps and the high flow-dynamic energy loss in the crossflow chamber:Hydroformylations on an industrial scale can scarcely be carried outeconomically in this device.

In view of this prior art, the object of the present invention is tospecify a device which permits homogeneous-catalytic gas/liquid phasereactions, in particular hydroformylations, which operate with membraneseparation of the catalyst, to be carried out on anindustrially-relevant scale economically.

This object is achieved by a device according to claim 1.

The invention therefore relates to a device for the continuoushomogeneous-catalytic reaction of a liquid with a gas and optionally afurther fluid, which device comprises at least one jet loop reactorhaving a pump-driven external liquid circuit and which comprises atleast one membrane separation stage that preferably retains thehomogeneous catalyst, and in which pump and membrane separation stageare arranged in the same external liquid circuit.

The invention is based on the knowledge that a jet loop reactor andnanofiltration may be combined to form a device which permits economiccarrying out of a hydroformylation on a commercial format. Fundamentalto the economic efficiency of the process is simple structure of theprocess with as few plant components as possible and also markedretention and recirculation of the active catalyst to the reaction. Aprocess reduced to the essential components results from the directintegration of the membrane separation into the external circuit of thejet loop reactor. This additionally permits separation of the catalystand optionally of the free ligand under reaction conditions.

Use of commercially available membrane modules for reaction mixtureshaving dissolved and/or non-dissolved gas fractions is not possible,since they are not designed for adequate permeate-side gas removal and,depending on the amount of the permeate-side gas volumetric flow rate tobe removed, build up a counterpressure on the permeate side whichdecreases the liquid permeate output or can even lead to destruction ofthe membrane. It has been found that using membrane modules which, persquare meter of active membrane area, a permeate-side free volume ofgreater than 0.3 cubic decimeter (dm³, equivalent to 1 liter) arenecessary for gas streams occurring on the permeate side. The greaterthe permeate-side gas stream, the greater must the free permeate-sidevolume be. Surprisingly, it has additionally been found that theretention of the catalyst, in process streams containing a gas phase atthe latest on the permeate side, is increased with the increase inpermeate-side free volume.

A particularly preferred development of the invention therefore providesthat a permeate-side free volume is provided in the membrane separationstage, which free volume is at least 0.3 dm³ per m² of membrane surface.

Permeate-side volume is taken to mean the volume following on thepermeate side perpendicular to the active membrane surface. Thepermeate-side free volume is the fraction of the permeate-side volumewhich is not filled with material apart from the permeate.

In a preferred embodiment of the invention, the pump is equippedstructurally for long-term pumping of fluids which contain liquid andgaseous phases. Particularly preferably, pumps should be used which inaddition can also transport a small solids fraction.

For this purpose, peripheral impeller pumps are particularly suitable.They can transport in the long term fluid mixtures which contain aliquid phase and a gaseous phase. Small solids fractions are not aproblem. A peripheral impeller pump is a particular type of acentrifugal pump having an annular peripheral channel in which the pumprotor rotates. The pump rotor is usually constructed as a circular diskhaving a multiplicity of radially extending projections on the disk. Theprojections run in the region of the peripheral channel. The fluid isdrawn in by suction through a suction port and passed through theannular channel in which the pump rotor rotates. This consists ofstraight paddles which place the fluid into a rotary motion. In theperipheral channel, therefore, the energy of motion is transferred fromthe paddles to the medium, as a result of which the pressure isincreased. The fluid leaves the peripheral impeller pump through anoutlet port after it has flowed through the peripheral channel.Peripheral impeller pumps are commercially available from K-ENGINEERINGMischtechnik and Maschinenbau, 26871 Papenburg (Germany) or from SPECKPUMPEN Verkaufsgesellschaft GmbH, 91231 Neunkirchen a. Sand (Germany).

In order to avoid deactivation of the catalyst and damage of themembrane due to degassing, and also to achieve an improved membraneretention, the permeate of the membrane separation stage needs to bedegassed in a controlled manner. In addition to the permeate-side freevolume dimensioned as above, a permeate-side gas discharge needs to beprovided arranged downstream of the membrane separation stage. Such agas discharge should be constructed as follows:

The core piece of the gas discharge is a compensating vessel in whichliquid and gaseous phases are separated from one another. The two-phasepermeate stream is fed to the vessel in order that liquid phase and gasphase can separate. A pressure maintaining device which removes gasuntil the preset pressure is reached is connected to the gas phase. Inaddition, a compressed gas feed is mounted on the vessel, whichcompressed gas feed permits the preset gas pressure to be held constant,for instance when the liquid level in the vessel is falling.

The suitable membrane material must be selected with respect to thecatalyst complex that is to be separated off: Since the permeability ofa membrane for the various components of the feed that is to beseparated is ultimately a function of time (the membrane is notabsolutely impermeable to a catalyst, its passage velocity is rathermarkedly slower in relation to the other reaction participants), themembrane must be selected in such a manner that the catalyst complexthat is to be separated off is retained preferentially.

In the process according to the invention membranes can be used which,owing to their chemical or physical properties, are suitable forretaining organophosphorus metal-complex catalyst and/or freeorganophosphorus ligand preferably to an extent of at least 50%.

Corresponding membranes belong to the class of nanofiltration membranes.The expression nanofiltration is applied to membrane separationprocesses which have a separation limit or molecular weight cutoff(MWCO) in the range from 150 g/mol to over 1 nm. The magnitude of theseparation limit or MWCO indicates the molecular or particle size of acomponent that has a membrane retention of 90%.

A usual method of determination for the separation limit is given in Y.H. See Toh, X. X. Loh, K. Li, A. Bismarck, A. G. Livingston, In searchof a standard method for the characterisation of organic solventnanofiltration membranes, J. Membr. Sci., 291 (2007) 120-125.

The membrane retention R_(i) is calculated from the feed-sideconcentration of the component i under consideration at the membranex_(IF) and the permeate-side concentration of component i underconsideration at the membrane x_(iP) as follows:R _(i)=1−x _(iP) /x _(iF)

Preferably, the membranes for the use according to the invention shouldhave an MWCO of less than 1000 g/mol.

A further precondition for the usability of the membrane is that themembrane must be stable to all compounds present in the reactionmixture, in particular to the solvents. Membranes are also considered tobe stable which experience a change with time of the MWCO and/or of thepermeability—for instance caused by swelling of the membrane polymer,but fulfill the separation task over the service life. Furthermore, themembrane material should withstand the reaction temperature. Membranematerials which are stable and perform well at the reaction temperaturepermit complex temperature control to be dispensed with.

Preferably, membranes are used which have an active separation layermade of a material selected from cellulose acetate, cellulosetriacetate, cellulose nitrate, regenerated cellulose, polyimides,polyamides, polyether ether ketones, sulfonated polyether ether ketones,aromatic polyamides, polyamide-imides, polybenzimidazoles,polybenzimidazolones, polyacrylonitrile, polyarylether sulfones,polyesters, polycarbonates, polytetrafluoroethylene, polyvinylidenefluoride, polypropylene, polydimethylsiloxane, silicones,polyphosphazenes, polyphenyl sulfides, polybenzimidazoles, 6.6 Nylon,polysulfones, polyanilines, polyurethanes, acrylonitrile/glycidylmethacrylate (PANGMA), polytrimethylsilylpropynes, polymethylpentynes,polyvinyltrimethylsilane, alpha-aluminum oxides, titanium oxides,gamma-aluminum oxides, polyphenylene oxide, silicon oxides, zirconiumoxides, silane-hydrophobized ceramic membranes, as are described inDE10308111, polymers having intrinsic microporosity (PIM) such as PIM-1and others, as are described, e.g., in EP0781166 and in “Membranes” byI. Cabasso, Encyclopedia of Polymer Science and Technology, John Wileyand Sons, New York, 1987. The abovementioned substances can be presentin crosslinked form in particular in the active separation layer,optionally by addition of auxiliaries, or as what are termed mixedmatrix membranes provided with fillers such as, e.g., carbon nanotubes,metal organic frameworks or hollow spheres and particles of inorganicoxides or inorganic fibers such as, e.g., ceramic or glass fibers.

Particularly preferably, membranes are used which have a polymer layerof polydimethylsiloxane, polyimide, polyamide-imide,acrylonitrile/glycidyl methacrylate (PANGMA), polyamide or polyetherether ketone as active separation layer and which are made up ofpolymers having intrinsic microporosity (PIM) such as PIM-1, or whereinthe active separation layer is built up over a hydrophobized ceramicmembrane. Very particularly preferably, membranes of silicones orpolyamide-imide are used. Such membranes are commercially available.

In addition to the abovementioned materials, the membranes can havefurther materials. In particular, the membranes can have support orcarrier materials on which the active separation layer is applied. Insuch composite membranes, in addition to the actual membrane, a supportmaterial is further present. A selection of support materials isdescribed in EP0781166, which is hereby explicitly incorporated byreference.

A selection of commercially available nanofiltration membranes are theMPF and Selro series from Koch Membrane Systems, Inc., various types ofSolsep BV, the Starmem™ series from Grace/UOP, the DuraMem™ and PuraMem™series from Evonik Industries AG, the Nano-Pro series from Bio-PureTechnology, the HITK-T1 from IKTS, and oNF-1, oNF-2 and NC-1 from GMTMembrantechnik GmbH.

According to a further preferred embodiment of the invention, a heatexchanger for heating or cooling the feed or the permeate of themembrane separation stage is arranged in the external liquid circuit, inparticular upstream of the membrane separation stage. The heat exchangergenerally serves for introducing heat energy into the system in the caseof endothermic reactions. In the case of exothermic reactions, the heatof reaction is removed via the heat exchanger.

Depending on the reaction temperature, placing the membrane separationupstream or downstream of the heat exchanger in the outer liquid circuitcan be advantageous for the membrane separation. Higher temperaturesgenerally lead to higher permeabilities, but, depending on the membranematerial, can lead to a reduction of the membrane retention.

In a further preferred embodiment of the invention, a tubular reactionspace extends in the jet loop reactor, into which tubular reaction spacea jet nozzle for injecting the liquid into the reaction space and also asuction tube for extracting the gas by suction both open out, and onwhich is provided a baffle plate-shielded takeoff for the externalliquid circuit.

The jet nozzle can be directed upwardly or downwardly in the verticallyextending reactor. The conjoint opening of jet nozzle and suction tubeeffects an intense mixing of the liquid and gaseous reaction components(water pump effect). The gas can be taken in via the suction tube fromthe outside, or from a region within the reaction space in which a gasbell extends. The takeoff can be arranged at the top or bottom on thereactor. The shielding of the takeoff by the baffle plate decreases theintroduction of gas bubbles from the internal liquid circuit into theexternal liquid circuit.

For improvement of flow dynamics, at least one guide tube which extendsconcentrically through the reaction space can be provided. The liquidand gaseous phase mixing is intensified thereby. Also, a plurality ofguide tubes can be arranged successively so as to align. The reactionmixture then flows through the guide tube in the main direction of flow,is reversed at the end of the guide tube and flows back outside theguide tube. The guide tube is a structural separation of the twodirections of flow of the internal loop.

When jet loop reactor and membrane separation stage are arranged in ashared external liquid circuit this means that the throughput throughreactor and membrane must be identical. For reasons of apparatus, thethroughput rate of reactor and membrane can be different, however. Inorder then, nevertheless, to implement a liquid circuit or idealmembrane overflow, it is possible to equip the apparatus with the lowthroughput rate using a bypass conduit which permits a partial bypass ofthe hydraulic obstacle. Accordingly, the device has at least one bypassconduit which is arranged in the external liquid circuit in parallel tothe jet loop reactor or to the membrane separation stage.

In a further preferred embodiment of the device, it has not only one,but a multiplicity of jet loop reactors that are connectable in paralleland have a shared external liquid circuit, wherein the membraneseparation stage is arranged within the shared external liquid circuit.A plurality of jet loop reactors that are specifically dimensioned to besmaller permit flexible adaptation of the throughput rate of the deviceto the demand state by connecting and disconnecting individual reactors.This permits economic utilization of the device in the case of changingdemand.

The membrane separation stage can accordingly also be constructed in aparallel manner: By connecting and disconnecting individual membranemodules connected in parallel, the entire membrane area of the membraneseparation stage can be flexibly adapted to the plant capacity. Apreferred development of the invention is therefore characterized by amembrane separation stage which comprises a multiplicity of membranesthat are connectable in parallel in such a manner that the entire activemembrane surface area of the membrane separation stage is adjustable byconnecting and disconnecting the membranes.

The device according to the invention is outstandingly suitable for thehomogeneous-catalytic reaction of a liquid with a gas and optionally afurther fluid, in which the target product of the reaction is dischargedfrom the liquid circuit with the permeate of the membrane separationstage.

The invention thus also relates to a process for thehomogeneous-catalytic reaction of a liquid with a gas and optionally afurther fluid, wherein the reaction is carried out in a device accordingto the invention, and wherein the target product of the reaction isdischarged from the liquid circuit together with the permeate of themembrane separation stage.

In particular when a membrane separation stage is used which has apermeate-side free volume of at least 0.3 dm³ per m² membrane area, itis possible to process a liquid circuit having a gaseous fraction. Thisis possible up to a gas fraction of about 30% by volume. In the case ofgas fractions of such a level, however, the permeate-side free volumemust be chosen to be markedly greater than 0.3 dm³. A preferreddevelopment of the process according to the invention is thus that theexternal liquid circuit upstream of the membrane separation stage is amixture which comprises a liquid phase and a gaseous phase disperselydistributed therein, wherein the volume fraction of the gaseous phase isbetween zero and thirty percent.

These reactions can be two-phase (liquid/gaseous) or three-phase(liquid/liquid/gaseous or liquid/gaseous/gaseous). In the liquidcircuit, small solids fractions can also be present.

Examples of the reactions which can be carried out are oxidations,epoxidations, hydroformylations, hydroaminations,hydroaminomethylations, hydrocyanations, hydrocarboxyalkylation,aminations, ammonoxidation, oximations, hydrosilylations, ethoxylations,propoxylations, carbonylations, telomerizations, methatheses, Suzukicouplings or hydrogenations.

Particularly preferably, the device is suitable for hydroformylation,that is for reacting compounds having olefinic double bonds withsynthesis gas to form aldehydes and/or alcohols.

The use of the described device for carrying out said processes islikewise subject matter of the invention.

The device according to the invention can be used, inter alia, forreacting a liquid with a gas, wherein both the gas and the liquid haveat least one reactant.

The reaction products are discharged in the liquid phase together withthe permeate.

In the apparatus according to the invention, reactions can be carriedout in the pressure range from 0.2 to 40 MPa (absolute) and in thetemperature range from 0 to 350° C. The reaction takes place in thiscase preferably in the presence of a catalyst that is homogeneouslydissolved in the liquid phase.

Preferably, in the device according to the invention, reactions arecarried out in which the catalyst is fed in together with the liquidfeed and is homogeneously dissolved in the liquid product/startingmaterial phase, such as, for example, the production of aldehydes and/oralcohols by hydroformylation of compounds having olefinic double bondsin the presence of cobalt or rhodium carbonyls with or without theaddition of phosphorus-containing ligands.

The invention will now be described in more detail with reference toexemplary embodiments. In the drawings:

FIG. 1: shows a device according to the invention having a jet loopreactor

FIG. 2: shows a device according to the invention having a plurality ofjet loop reactors

FIG. 3: shows a device according to the invention having a plurality ofbypass options;

FIG. 4: shows a schematic of a degassing;

FIG. 5: shows a schematic of permeate-side free volume in the case of amembrane having a permeate placeholder;

FIG. 6: shows a schematic of permeate-side free volume in the case of amembrane without permeate placeholder;

FIG. 7: shows a tubular membrane module, schematically in axial view;

FIG. 8: shows a tubular membrane module of FIG. 7 in longitudinalsection;

FIG. 9: shows a tubular membrane module comprising a bundle of tubularmembranes;

FIG. 10: shows a tubular membrane module comprising a bundle of tubularmembranes having a shared support structure.

FIG. 1 shows a first embodiment of the device according to the inventionhaving a jet loop reactor 1. The jet loop reactor 1 comprises a tubularreaction space 2 in the form of a pressure tube which is filled withliquid reaction mixture up to a defined liquid level 3. A gas bell ofgaseous reaction participants forms above the liquid level. On accountof the dissolution equilibrium, the gaseous reaction participants are inpart dissolved in the liquid reaction mixture, and in part gaseousreaction participants are located as gas phase in the liquid (in thedrawing shown as gas bubbles). Also dissolved in the reaction liquid isthe homogeneous catalyst.

A jet nozzle 4 projects downwards into the liquid reaction mixture, viawhich jet nozzle liquid reaction participants are injected with highkinetic energy Gaseous reaction participants pass through a gas feed 5into the reaction space 2. A suction tube is assigned structurally tothe steel nozzle 4, which suction tube takes in by suction the gas fromthe gas-filled part of the reaction space 2 and mixes it with the fluidstream. The orifices of suction tube and jet nozzle are closely adjacentfor this purpose and open out together into the reaction space. Thegaseous reaction participants are entrained by the high flow velocity ofthe liquid reaction participants exiting from the jet nozzle 4(comparable with a water-jet pump).

A guide tube 6 extends concentrically and coaxially to the pressure tubethrough the reaction space 2. The guide tube 6 serves for creating aninternal liquid circuit within the reaction space 2: The injectedreaction liquid flows from the jet nozzle 4 down through the guide tube6 and is reversed by the baffle plate 7 arranged at the other end of thereaction space 2, in such a manner that the stream flows back up outsidethe guide tube 6. In this manner an internal liquid circuit is formedwithin the reaction space 2, in which internal liquid circuit thereaction partners are intensely mixed and reacted.

Below the baffle plate 7 a takeoff 8 is provided, through which reactionmixture is continuously taken off from the reaction space 2 and fed intoan external liquid circuit 9. The baffle plate 7 shields the takeoff 8for the internal liquid circuit in such a manner that gas bubblesscarcely pass into the external liquid circuit 9. The external liquidcircuit therefore predominantly comprises liquid reactants, dissolvedcatalyst and dissolved gaseous reactants.

For performance of the invention it is unimportant whether jet nozzle 4is directed downwards and baffle plate 7 is arranged below the jetnozzle 4. It is also possible to inject upwards from the bottom of thereactor. The takeoff can be arranged in both cases at the top or bottomin the reactor. The baffle plate must correspondingly be arranged insuch a manner that it shields the takeoff.

The external liquid circuit 9 is moved by a pump 10. The pump 10 is aperipheral impeller pump which is also able to transport liquid/gaseousmixtures. Insignificant gas bubbles are therefore harmless.

A heat exchanger 11 is arranged downstream of the pump 10, by means ofwhich heat exchanger, depending on the type of reaction, heat can beintroduced into or discharged from the external liquid circuit 9.Furthermore, the jet loop reactor 1 can itself be provided with a heatexchanger (which is not shown) which surrounds the reaction space.

A membrane separation stage 12 is arranged downstream of the heatexchanger 11. The membrane separation stage can also be situatedupstream of the heat exchanger. As with any membrane, the membraneseparation stage 12 has three connections, namely feed 13, permeate 14and retentate 15. The reaction mixture flowing in via the feed 13 isseparated at the membrane into permeate 14 and retentate 15. Since themembrane is less permeable to the dissolved catalyst complex than to theremaining feed components, the catalyst remains this side of themembrane and is enriched in the retentate 15. In relation to thecatalyst, the membrane has a better permeability to the products ofvalue, and so the products of value are enriched in the permeate 15relative to the catalyst. The permeate 14 is conducted further forworkup (not shown); the catalyst-rich retentate 15 is returned to thereactor 1 mixed with fresh liquid starting material 16 via the jetnozzle 4.

In order to prevent damage to the membrane and deactivation of thecatalyst, uncontrolled degassing of dissolved gaseous reactionparticipants must be avoided at the membrane 12 and a minimum CO partialpressure in the permeate 14 must be ensured. This is achieved by aseparately provided degassing element (see below under FIG. 4) and/or bysuitable dimensioning of the free volume of the membrane (see belowunder FIGS. 5 to 10). In addition, the shielding of the takeoff 8 bymeans of a baffle plate 7 aids avoiding as far as possible gas bubblesin the feed 13 to the membrane separation stage 12.

FIG. 2 shows a second embodiment of the device according to theinvention. It comprises three parallel-connected jet loop reactors 1,17, 18, each of which is constructed as for the described first jet loopreactor 1. All three jet loop reactors 1, 17, 18 share the jointexternal liquid circuit 9 in which pump 10, heat exchanger 11 andmembrane separation stage 12 are used jointly. The advantage of theparallel arrangement is a better adaptability of the plant to changingdemand: At base load, two jet loop reactors 1, 17 should run, at highdemand the third 18 can be connected in, and at low demand the second 17is also disconnected, in such a manner that the plant operates with onlyone reactor 1. The reactors 1, 17, 18 must correspondingly be providedwith suitable disconnecting elements (which are not shown). Owing to theswitchable parallel connection, a better plant utilization is possible.Furthermore, each individual (connected) reactor can always be operatedin the optimum operating state with respect to flow dynamics. Partialload operation is very largely prevented. By changing the speed ofrotation, the pump is adapted to the respective volumetric flow rates.The adaptation of the total active surface area of the membraneseparation stage is likewise possible by suitable parallel connection ofa plurality of membranes.

FIG. 3 shows various developments of the invention, each of which has abypass conduit 19 a, 19 b, 19 c, 19 d.

As described above, the plant according to this embodiment alsocomprises a jet loop reactor 1, in the external liquid circuit 9 ofwhich is arranged a pump 10 and a membrane separation stage 12 forremoving the product together with the permeate 14. Starting material 16is injected into the reactor 1. An optional heat exchanger 11 can bearranged in the feed 14 or in the retentate 15 of the membraneseparation stage 15. A precondition of the maintenance of the liquidcircuit 9 is that the mass throughput through the reactor 1 is the sameas through the membrane (starting material 16 and product in thepermeate 14 balance out). Since the residence time in the reactor candemand a different mass flow rate, however, than the ideal membraneoverflow offers, depending on the process, a bypass conduit 19 isnecessary, each of which runs in parallel to the “slower” plant element.Thus, bypass 19 a can run in parallel to the slower reactor 1; in theevent that the reactor is faster, the bypass 19 b must be arranged inparallel to the membrane separation stage 12. If the heat exchanger 11is the limiting factor, bypass 19 c must be provided in the feed for theheat exchanger, or bypass 19 d must be provided in the retentate for theheat exchanger. In each case a corresponding substream flows through thebypass round the respective plant element. The other part of courseflows further through the element. The bypass is therefore not acomplete bridging, but merely opens a hydraulically expedientalternative path.

FIG. 4 shows an optional degassing 20 which can be arranged in thepermeate stream 14 of the membrane separation stage in order to preventuncontrolled degassing at the membrane. The degassing comprises apressure vessel 21 in which a liquid phase I and a gaseous phase gseparate from one another. The product-containing liquid phase I istaken off via a product takeoff 22. The pressure of the gaseous phase iscontrolled by throttles 23, 24. If the pressure is excessive, gas istaken off via throttle 23. If the pressure in the vessel falls, whichcan lead to degassing at the membrane, the pressure vessel 21 is chargedwith gas from the outside via throttle 24. The transmembrane pressure ofthe membrane separation stage 12 can also be adjusted via the degassing20.

Since commercially available membrane modules are not able to passthrough gas fractions in the liquid stream in the long term withoutdamage, according to the invention it is proposed to dimension thepermeate-side free volume with at least 0.3 dm³ per m² of membrane area.The free permeate-side volume is explained with reference to FIGS. 5 to10.

FIG. 5 shows the schematic structure of a planar membrane separationstage. The membrane comprises an active separation layer 25 and a poroussupport layer 26 arranged downstream with the permeate. The separationtakes place at the active separation layer 25, the support layer 26mechanically stabilizes the active separation layer 25. The membranemodule is either symmetrically constructed (line of symmetry 27) orunsymmetrically constructed. In this case, line 27 denotes the oppositewall of the membrane module. A permeate placeholder 28 (also termedpermeate spacer) can be provided with the permeate further downstream,for example a coarsely porous structure or a grating or a mesh.

The feed 13 flows along the active separation layer 25, is depleted inthe permeating components thereof, and leaves the membrane as retentate15. The permeate 14 passes through the active separation layer 26 andleaves the membrane separation stage. The permeate-side volume V_(P) isunderstood as the permeate-side volume following perpendicularly to theactive membrane surface area O_(A) (surface area of the activeseparation layer 25). This extends along the height h up to the line ofsymmetry or wall 27 of the membrane separation stage. Thus, for planarmembrane systems, or else in approximation to flat channel systems aswith the spiral wound element, the following applies:V _(P) =O _(A) ×h.

The free permeate-side volume V_(Pf) is the fraction of thepermeate-side volume V_(P) which is not filled by the material of theactive separation layer 25, the support layer 26 and the permeateplaceholder 28. In operation, this space is occupied by permeate. It mayaccordingly be measured volumetrically by charging a test liquid (termed“volumetric measurement”).

The free permeate-side volume V_(Pf) is adjusted by dimensioning thepermeate placeholder 28 since the porosity of the active separationlayer 25 is determined by the separation task and that of the supportlayer 26 by the mechanical load.

The permeate-side free volume V_(Pf) must be adjusted according to theinvention in such a manner that the following applies:V _(Pf) [dm³]≧0.3×O _(A) [M²]

Dispensing with a permeate placeholder shown in FIG. 6 increases thepermeate-side free volume V_(Pf), provided that the remaining dimensionsof the membrane are retained.

In FIGS. 5 and 6, flow passed through the membrane from the outside tothe inside. There are also membrane modules in which flow passes throughthe membranes from the inside to the outside. Thus, FIG. 7 outlines atubular membrane module in which feed 13 and permeate 15 flow axiallythrough a cylindrical inner channel 29 which is surrounded by the activeseparation layer 25. The support layer 26 follows this radially towardsthe exterior. The permeate 14 flows off from the membrane module throughan annular outer channel 30 which surrounds the support layer 26 and isitself sealed off from the outside by the wall 27 of the membranemodule. The permeate-side volume V_(P) is thus calculated from theproduct of the active membrane surface area O_(A) and the height h.

FIG. 8 shows a longitudinal section through the tubular membrane moduleof FIG. 7.

FIG. 9 shows a variant of a tubular membrane module in which amultiplicity of cylindrical inner channels 29 are bundled within thewall 27 of a tube. Each inner channel 29 is surrounded by a cylindricalactive separation layer 25 and a cylindrical support layer 26. Incalculation of the permeate-side volume, therefore, the packing densityof the channels 29 must be taken into account. For the active membranesurface area O_(A), the total of the shell surfaces of the innerchannels 29 formed by the active separation layer 25 must be formulated.A switchable parallel connection of the membranes may be effected byoptional disconnection of the individual inner channels 29 by suitabledisconnecting elements. Flexible adaptation of the entire active surfacearea of the membrane separation stage to the demand situation is therebypossible.

FIG. 10 shows a further variant of a tubular membrane module in which amultiplicity of inner channels 29 are bundled within the wall 27 of atube, wherein the inner channels 29, however, share a common supportstructure 26.

Using the combination according to the invention of a jet loop reactorwith a membrane separation stage, gas/liquid reactions, in particularhydroformylations, may be carried out more economically than withreactors traditionally used in the industry.

EXAMPLES

1. Membrane Pretesting

Studies on permeate flux determination and retention measurement werecarried out for preselecting suitable membranes. A 1-pentenehydroformylation reaction mixture was charged into a 5 l reservoir. Thecomposition of the reaction mixture is given in table X. As catalystligand system, 10 mg/kg of rhodium and 1170 mg/kg of Alkanox P-24 (CASNo. 26741-53-7) are present.

TABLE X 1-Pentene 2-Methylpentanal Hexanal Remainder [% by wt.] [% bywt.] [% by wt.] [% by wt.] 6.996 47.960 43.932 1.112 6.894 47.774 43.5851.747

The reaction mixture was conducted over the tested membranes at 25° C.,a transmembrane pressure difference of 4 bar and an overflow of 200 l/h.

TiO₂ monochannel membranes of the Innopor® nano type having a medianpore size of 0.9 nm, a separation limit of 450 Da and an open porosityof 0.3 to 0.4 from Innopor GmbH were tested. At a channel length of 500mm and an internal diameter of 7 mm, an active membrane surface area ofapproximately 100 cm² results.

The results of the permeability measurements are shown in table Y.Permeabilities in two different orders of magnitude result. Four ofeight tested membranes are in the range from 0.8 to 2.9 kg/(m² h bar).The other four membranes are in the range from 18 to 37 kg/(m² h bar).

TABLE Y Membrane Permeability Number [kg/(m²h bar)] 1 0.8 2 19 3 37 4 185 29 6 1.6 7 1.5 8 2.9

In a further test for determining retention, isopropanol was chargedinto the reservoir. Rose bengal (CAS No. 11121-48-5) having a molar massof 974 g/mol was used as a marker for determining retention. Retentionsfrom 93 to 97% were found for the membranes having permeabilities in therange from 0.8 to 2.9 kg/(m²h bar). For the membranes havingpermeabilities in the range from 18 to 37 kg/(m²h bar), retentions from55 to 61% were found. Since the membranes, according to themanufacturer's instructions, should have a separation limit of 450g/mol, the membranes having high permeability and low retention for Rosebengal were rejected as defective.

2. Example According to the Invention (0.9 nm)

In an experimental plant as shown in FIG. 1 having a jet loop reactor(1), hydroformylation reactions of 1-pentene (16) with synthesis gas (5)to give the corresponding aldehyde isomers were carried out. In theliquid circuit (9) driven by a peripheral impeller pump (10), thecatalyst-ligand system was separated off and returned by means of amembrane separation stage (12) for continuous reuse of thecatalyst-ligand system in the hydroformylation reaction in the jet loopreactor (1).

For the reaction, 1-pentene (16) was fed to the reactor in the absenceof oxygen continuously via the permeate of the membrane separation stagein accordance with the reaction product removal. The catalyst precursorwas rhodium acetylacetonatodicarbonyl (CAS No. 14847-82-9). The ligandused was Alkanox P-24 (CAS No. 26741-53-7). The rhodium concentrationand the ligand concentration in the loop reactor was held constant at 10mg/kg and 1170 mg/kg, respectively, by continuous replenishment. Thereaction was carried out under 50 bar synthesis gas pressure (CO/H₂,mass ratio 1:1) at 110° C.

The reaction product was continuously conducted through a membraneseparation stage (12) constructed as a one-stage nanofiltrationmembrane. The transmembrane pressure required is built up by the reactorpressure and a controlled permeate-side (14) pressure. The desiredoverflow of 500 kg/h over the high-pressure side of the membrane isadjusted via the peripheral impeller pump.

Membrane number 1 of example 1 was installed in the membrane module ofthe membrane separation stage (12).

At a channel length of 500 mm and an internal diameter of 7 mm, anactive membrane surface area of approximately 100 cm² results. Thepermeate-side free volume based on the membrane area is greater than 0.5dm³/m². The overflow over the membrane was 4.4 m/s. The temperature inthe membrane separation step was 102° C. A synthesis gas pressure(CO/H₂, mass ratio 1:1) of 10 bar was held on the permeate side using adevice according to FIG. 4 for stabilizing the catalyst-ligand complex,as a result of which a transmembrane pressure of 40 bar was set at aretentate-side pressure of 50 bar. The low pressure of the permeate sideleads to outgassing of synthesis gas. The two-phase permeate stream (14)is fed to a degassing appliance (FIG. 4).

Permeate (14) which consists predominantly of reaction product waswithdrawn from the system via the membrane in the membrane separationstage. The catalyst and the ligand Alkanox were very largely retained bythe membrane and accumulate in the retentate (15). The retentate (15)was continuously fed back to the jet loop reactor (1).

The process chain was evaluated on the basis of measurement andanalytical data which were obtained by gas-chromatographic analysis,HPLC analysis, atomic absorption spectroscopy and optical emissionspectrometry with inductively coupled high-frequency plasma. Thereaction was studied with respect to the conversion rate of 1-penteneand also the yield and selectivity of aldehyde. The membrane separationstage (12) was studied with respect to permeate flux and retention ofrhodium and ligand. The conversion rate of 1-pentene was 95%, and thealdehyde selectivity was 98%.

The TiO₂ monochannel membrane of the Innopor® nano type showed amembrane retention rate between 88 and 92% with respect to the rhodiumat specific permeate flux output between 53 and 57 kg/m² h. Theretention of the ligand was 83%.

The example shows that the homogeneous catalyst could be quantitativelyretained and recirculated to the loop reactor using the selectedmembrane separation stage in the liquid circuit of the loop reactor. Thespecific free permeate volume of the membrane separation stage which wassufficiently high made possible a high retention of the catalyst systemand enabled an unrestrictedly good permeate flux despite thepermeate-side degassing. In addition, the catalyst was retained inactive form with a nanofiltration under the selected conditions.

3. Example According to the Invention (3 nm)

1-Pentene (16) hydroformylation reactions with synthesis gas (5) to givethe corresponding aldehyde isomers were carried out in an experimentalplant as shown in FIG. 1 having a jet loop reactor (1). Thecatalyst-ligand system was separated off and recirculated in the liquidcircuit (9) driven by a peripheral impeller pump (10) by means of amembrane separation stage (12) for continuous reuse of thecatalyst-ligand system in the hydroformylation reaction in the jet loopreactor (1).

For the reaction, 1-pentene (16) was fed continuously to the reactor inthe absence of oxygen via the permeate of the membrane separation stagein accordance with the reaction product removal. The catalyst precursorwas rhodium acetylacetonatodicarbonyl (CAS No. 14847-82-9). The ligandused was Alkanox P-24 (CAS No. 26741-53-7). The rhodium concentrationand the ligand concentration in the loop reactor were held constant at10 mg/kg and 1170 mg/kg, respectively, by continuous replenishment. Thereaction was carried out at 50 bar synthesis gas pressure (CO/H₂, massratio 1:1) at 110° C.

The reaction product was conducted continuously through a membraneseparation stage (12) constructed as a one-stage nanofiltrationmembrane. The transmembrane pressure required is built up by the reactorpressure and a controlled permeate-side (14) pressure. The desiredoverflow of 500 kg/h over the high-pressure side of the membrane isestablished via the peripheral impeller pump.

A prototype of a membrane hydrophobized by silanization was built intothe membrane module of the membrane separation stage (12) as amonochannel tube by the Fraunhofer-Institut für Keramische Technologienand Systeme IKTS [Fraunhofer Institute for Ceramic Technologies andSystems]. The carrier consisted of Al₂O₃ having a median pore size of 3μm and a hydrophobized membrane layer based on a ZrO₂ layer having amedian pore diameter of 3 nm.

At a channel length of 500 mm and an internal diameter of 7 mm, anactive membrane area of approximately 100 cm² results. The permeate-sidefree volume based on the membrane area is greater than 0.5 dm³/m². Theoverflow across the membrane was 4.4 m/s. The temperature in themembrane separation step was 101° C. A synthesis gas pressure (CO/H₂,mass ratio 1:1) of 10 bar was held for stabilizing the catalyst-ligandcomplex on the permeate side using a device according to FIG. 4, as aresult of which a transmembrane pressure of 40 bar was established at aretentate-side pressure of 50 bar. The low pressure of the permeate sideleads to outgassing of synthesis gas. The two-phase permeate stream (14)is fed to a degassing appliance (FIG. 4).

Permeate (14) which predominantly comprises reaction product was takenoff from the system in the membrane separation stage. The catalyst andthe ligand Alkanox were very largely retained by the membrane andaccumulate in the retentate (15). The retentate (15) was continuouslyreturned to the jet loop reactor (1).

The process chain was evaluated on the basis of measurement andanalytical data which were obtained by gas-chromatographic analysis,HPLC analysis, atomic absorption spectroscopy and optical emissionspectrometry with inductively coupled high-frequency plasma. Thereaction was studied with respect to the conversion rate of 1-penteneand the yield and selectivity of aldehyde. The membrane separation stage(12) was studied with respect to permeate flux and retention of rhodiumand ligand. The conversion rate of 1-pentene was 94%, and the aldehydeselectivity was 98%.

The prototype membrane showed a membrane retention with respect torhodium between 73 and 74% at specific permeate flux outputs between 96and 98 kg/m²h. The retention of the ligand was 64%.

Example 2 also shows that the homogeneous catalyst was able to beretained quantitatively and returned to the loop reactor using theselected membrane separation stage in the liquid circuit of the loopreactor. The specific free permeate volume of the membrane separationstage that is sufficiently high permitted a high retention of thecatalyst system and an unrestrictedly good permeate flux despite thepermeate-side degassing. In addition, the catalyst was retained inactive form using a nanofiltration under the selected conditions.

4. Example

In this example the effect of gas loading under conditions as constantas possible in the membrane separation stage with respect to retentatepressure, permeate pressure and temperature is to be demonstrated. Forthis purpose the experimental setup of example 2 and example 3 accordingto FIG. 1 was extended by a pressurizing pump in the liquid circuit (9)downstream of the loop reactor (1) and upstream of the bypass conduit(19 a, FIG. 3). This is necessary, since the feed pressure of themembrane should sometimes be above the synthesis gas pressure in thereactor in the experiments. The peripheral impeller pump (10) inaddition generates the overflow of the membrane separation stage.

1-Pentene (16) hydroformylation product according to the composition oftable X of example 1 was charged in the jet loop reactor (1). Thecatalyst-ligand system was separated off and returned to the jet loopreactor (1) by means of a membrane separation stage (12) for thecatalyst-ligand system in the liquid circuit (9) driven by theperipheral impeller pump (10).

The synthesis gas pressure (CO/H₂, mass ratio 1:1) was varied in the jetloop reactor (1) from 10, 20, 30, 40, 50 bar.

The reaction product charged with synthesis gas was continuouslyconducted via a membrane separation stage (12) constructed as aone-stage nanofiltration membrane. The transmembrane pressure requiredis held at 40 bar by the additional pump in the liquid circuit. Thedesired overflow of 500 kg/h over the high-pressure side of the membraneis established via the peripheral impeller pump.

Membrane number 1 of example 1 was installed in the membrane module ofthe membrane separation stage (12). At a channel length of 500 mm and aninternal diameter of 7 mm, an active membrane area of approximately 100cm² results. The permeate-side free volume based on the membrane area isgreater than 0.5 dm³/m². The overflow over the membrane was 4.4 m/s. Thetemperature in the membrane separation step was 60° C. A synthesis gaspressure (CO/H₂, mass ratio 1:1) of 10 bar was held on the permeate sideusing a device according to FIG. 4 to stabilize the catalyst-ligandcomplex, as a result of which a transmembrane pressure of 40 bar was setat a retentate-side pressure of 50 bar. The low pressure of the permeateside leads to a corresponding amount of outgassing synthesis gas on thepermeate side, depending on the level of the synthesis gas pressure inthe loop reactor. The two-phase permeate stream (14) is fed to adegassing appliance (FIG. 4).

Permeate (14) which predominantly comprises reaction product was takenoff from the system via the membrane in the membrane separation stage.The rhodium complex and the free ligand were very largely retained bythe membrane and accumulate in the retentate (15). The retentate (15)was continuously returned to the jet loop reactor (1).

The process chain was evaluated on the basis of measurement andanalytical data which were obtained by gas-chromatographic analysis,HPLC analysis, atomic absorption spectroscopy and optical emissionspectrometry with inductively coupled high-frequency plasma. Themembrane separation stage (12) was studied with respect to permeate fluxand retention of rhodium and ligand. The results of the example aresummarized in table Z1:

TABLE Z1 Synthesis gas TMP Temperature Permeate flux Rh retention [bar][bar] [° C.] [kg/(m²h)] [%] 10 40 60 28.2 91.1 20 40 60 30.1 89.8 30 4060 29.4 90.5 40 40 60 28.4 91.3 50 40 60 29.7 90.0

This example shows that the synthesis gas pressure in the reactor andthus the amount of dissolved synthesis gas has no effect on the permeateflux at a permeate-side free volume of greater than 0.5 dm³/m² based onthe membrane area.

5. Counterexample in the Membrane Coil

In this example, the effect of gas loading under conditions as constantas possible in the membrane separation stage with respect to retentatepressure, permeate pressure and temperature is to be demonstrated. Forthis purpose, the experimental setup of example 2 and example 3according to FIG. 1 was extended by a pressurizing pump in the liquidcircuit (9) downstream of the loop reactor (1) and upstream of thebypass conduit (19 a, FIG. 3). This is necessary, since in theexperiments the feed pressure of the membrane should sometimes be abovethe synthesis gas pressure in the reactor. The peripheral impeller pump(10) continues to generate the overflow of the membrane separationstage.

1-Pentene (16) hydroformylation product according to the composition oftable X of example 1 was charged in the jet loop reactor (1). In theliquid circuit (9) driven by the peripheral impeller pump (10), thecatalyst-ligand system was separated and returned to the jet loopreactor (1) by means of a membrane separation stage (12) for thecatalyst-ligand system. The synthesis gas pressure (CO/H₂, mass ratio1:1) was varied in the jet loop reactor (1) from 10, 20, 30, 40, 50 bar.

The reaction product charged with synthesis gas was conductedcontinuously via a membrane separation stage (12) constructed as aone-stage nanofiltration membrane. The transmembrane pressure requiredis kept at 40 bar by the additional pump in the liquid circuit. Thedesired overflow of 250 kg/h over the high-pressure side of the membraneis set via the peripheral impeller pump.

A 1.8″ times 12″ membrane spiral coil having a membrane of the ONF2 typefrom GMT Membrantechnik GmbH was installed in the membrane module of themembrane separation stage (12). The feed spacer had a height of 31 mmand the permeate spacer had a height of 10 mm. This gives an activemembrane area of approximately 0.1 m². The permeate-side free volumebased on the membrane area is less than 0.1 dm³/m². The temperature inthe membrane separation step was 60° C. A synthesis gas pressure (CO/H₂,mass ratio 1:1) of 10 bar was held on the permeate side using a deviceaccording to FIG. 4 for stabilizing the rhodium-ligand complex, as aresult of which, at a retentate-side pressure of 50 bar, a transmembranepressure of 40 bar was established. The low pressure of the permeateside leads to a corresponding amount of outgassing synthesis gas on thepermeate side, depending on the height of the synthesis gas pressure inthe loop reactor. The two-phase permeate stream (14) is conducted to adegassing appliance (FIG. 4).

In the membrane separation stage, permeate (14) that predominantlycomprises reaction product was taken off from the system via themembrane. The rhodium complex and the free ligand were very largelyretained by the membrane and accumulate in the retentate (15). Theretentate (15) was continuously returned to the jet loop reactor (1).

The process chain was evaluated on the basis of measurement andanalytical data which were obtained by gas-chromatographic analysis,HPLC analysis, atomic absorption spectroscopy and optical emissionspectrometry with inductively coupled high-frequency plasma. Themembrane separation stage (12) was studied with respect to permeate fluxand retention for rhodium and ligand. The results of the example aresummarized in table Z2:

TABLE Z2 Synthesis gas TMP Temperature Permeate flux Rh retention [bar][bar] [° C.] [kg/(m²h)] [%] 10 40 60 114 96.4 20 40 60 114 94.8 30 40 60113 96.3 40 40 60 101 93.3 50 40 60 79 94.0

This example shows that the synthesis gas pressure in the reactor andthus the amount of dissolved synthesis gas has an effect on the permeateflux. The more synthesis gas can outgas on the permeate side of themembrane, the lower is the permeate flux of the membrane. In theexample, the permeate flux at a synthesis gas pressure typical of thereaction of 50 bar is 31% lower than at a synthesis gas pressure of 10to 20 bar in the reactor. The cause of this is the insufficientpermeate-side volume of less than 0.1 dm³/m².

6. Example: Long-Term Testing

The membrane of example 5 was studied in a long-term experiment. Thereaction procedure corresponds to examples 2 and 3. The reaction wascarried out under 50 bar synthesis gas pressure (CO/H₂, mass ratio 1:1)at 110° C.

The reaction product was first conducted through a heat exchanger (11,FIG. 3) and then through a membrane separation stage (12) constructed asa one-stage nanofiltration membrane. The temperature in the membraneseparation step was 60° C. The required transmembrane pressure is builtup by the reactor pressure and a controlled permeate-side (14) pressure.The desired overflow of 250 kg/h over the high-pressure side of themembrane is established via the peripheral impeller pump. A synthesisgas pressure (CO/H₂, mass ratio 1:1) of 10 bar was held on the permeateside for stabilizing the rhodium-ligand complex using a device accordingto FIG. 4, as a result of which a transmembrane pressure of 40 bar wasestablished at a retentate-side pressure of 50 bar. The low pressure ofthe permeate side leads to outgassing of synthesis gas. The two-phasepermeate stream (14) is conducted to a degassing appliance (FIG. 4). Asecond heat exchanger (11, FIG. 3) in the liquid circuit heats thecircuit back to reaction temperature.

Permeate (14) that predominantly comprises reaction product waswithdrawn from the system via the membrane in the membrane separationstage. The rhodium complex and the free ligand were very largelyretained by the membrane and accumulated in the retentate (15). Theretentate (15) was continuously returned to the jet loop reactor (1).

The process chain was evaluated on the basis of measurement andanalytical data which were obtained by gas-chromatographic analysis,HPLC analysis, atomic absorption spectroscopy and optical emissionspectrometry with inductively coupled high-frequency plasma. Thereaction was studied with respect to the conversion rate of 1-penteneand also the yield and selectivity of aldehyde. The membrane separationstage (12) was studied with respect to permeate flux and retention ofrhodium and ligand. The conversion rate of 1-pentene was 93% and thealdehyde selectivity was 98%.

The ONF2 membrane coil exhibited at specific permeate flux outputsbetween 73 and 77 kg/m²h. The rhodium retention decreased onlyinsignificantly from 93 to 94% in the course of 9 weeks to 90%. In the10^(th) week, however, a retention of only 34% was measured. Suchmembrane damage does not occur in the case of a single-phase flow in thepermeate space of such a membrane coil.

LIST OF REFERENCE SIGNS

1 Jet loop reactor

2 Reaction space

3 Liquid level

4 Jet nozzle

5 Gas feed

6 Guide tube

7 Baffle plate

8 Takeoff

9 External liquid circuit

10 Pump

11 Heat exchanger

12 Membrane separation stage

13 Feed

14 Permeate

15 Retentate

16 Starting material

17 Second jet loop reactor

18 Third jet loop reactor

19 Bypass conduit

20 Degassing

21 Pressure vessel

22 Product takeoff

23 Throttle gas takeoff

24 Throttle gas addition

g Gaseous phase in the pressure vessel

l Liquid phase in the pressure vessel

25 Active separation layer

26 Support layer/support structure

27 Line of symmetry/wall

28 Permeate placeholder

V_(P) Permeate-side volume

V_(Pf) Permeate-side free volume

O_(A) Active membrane surface area

h Height

29 Inner channel

30 Outer channel

The invention claimed is:
 1. A device, comprising: a reactor having a pump-driven external liquid circuit; and a membrane separation stage configured to retain a homogeneous catalyst, wherein the reactor is a jet loop reactor, the pump and membrane separation stage are configured in the same external liquid circuit, and a permeate-side free volume is in the membrane separation stage, wherein a free volume is at least 0.3 dm³ per m² of a membrane surface.
 2. The device of claim 1, wherein the pump is equipped structurally long-term pumping of fluids which comprise liquid and gaseous phases.
 3. The device of claim 2, wherein the pump is a peripheral impeller pump.
 4. The device of claim 1, wherein a permeate-side gas discharge is configured downstream of the membrane separation stage.
 5. The device of claim 1, wherein a heat exchanger adapted for heating or cooling a feed or a permeate of the membrane separation stage is arranged in the external liquid circuit.
 6. The device of claim 1, wherein a tubular reaction space extends in the jet loop reactor, into which a jet nozzle adapted for injecting liquid into the reaction space and a suction tube adapted for extracting gas by suction both open out, and on which is a baffle plate-shielded takeoff adapted for the external liquid circuit.
 7. The device of claim 1, wherein a bypass conduit which is arranged in the external liquid circuit is parallel to the jet loop reactor or to the membrane separation stage.
 8. The device of claim 1, comprising a multiplicity of jet loop reactors that are connectable in parallel and have a shared external liquid circuit, wherein the membrane separation stage is arranged within the shared external liquid circuit.
 9. The device of claim 8, wherein the membrane separation stage comprises a multiplicity of membranes that are connectable in parallel in such a manner that an entire active membrane surface area of the membrane separation stage is adjustable by connecting and disconnecting the membranes.
 10. The device of claim 1, wherein the device is suitable for carrying out a homogeneous-catalytic reaction.
 11. The device of claim 1, wherein a heat exchanger adapted for heating or cooling a teed or a permeate of the membrane separation stage is arranged in the external liquid circuit, upstream of the membrane separation stage.
 12. The device of claim 1, wherein the free volume is at least 0.5 dm³ per m² of a membrane surface.
 13. The device of claim 1, wherein the membrane separation stage comprises at least one membrane having a molecular weight cutoff in the range of 150 g/mol to less than 1000 g/mol.
 14. The device of claim 13, wherein the free volume is at least 0.5 dm³ per m² of a membrane surface. 